The annual U.S. incidence rate of head and neck cancer is approximately 40,000 cases (Vokes et al., New Eng. J. Med., 328: 184 (1993)). Although salivary gland tumors differ in their etiology, histology and standard therapy from most head and neck cancer, these cancers represent a significant threat to human health. Salivary gland tumors arise from either one of the three major salivary glands or from the minor salivary glands that line the mucosa of the upper aerodigestive tract. Histologically, these tumors are very heterogenous, and include mucoepidermoid cancers, pleomorphic adenoma, and adenoid cystic carcinomas as the more frequent observed tumor types. Treatment of these tumors is predominantly surgical, with post-operative radiotherapy being frequently administered. For unresectable tumors, neutron irradiation has been used in place of conventional radiotherapy. Chemotherapy is typically reserved for patients with recurrent or metastatic disease.
Mucoepidermoid carcinoma is the most common malignant human salivary gland tumor, which can arise from both major (parotid) and minor salivary glands, including serous/mucous glands within the pulmonary tracheobronchial tree (Calcaterra, in Cancer Treatment, 4th ed. (Haskell, ed.), W. B. Saunders Company, Philadelphia (1995), at pages 721-726). These salivary gland tumors can be deadly, due to their tendency to grow locally and recur aggressively, if not completely excised. However, complete excision is difficult due to the three-dimensional growth pattern of these tumors, which makes it difficult for the surgeon to determine accurately when clean margins have been achieved. Pathologic analysis using light microscopy is currently employed to assess tumor margins and to help determine the need for post-operative radiotherapy. However, this approach does not necessarily provide sufficient sensitivity for optimal patient management. In addition, both surgeons and patients desire minimal surgical approaches for cosmetic reasons, as well as to preserve nerve function to the facial area.
A chromosomal translocation has been implicated in certain forms of cancer. See, Tonon et al., “t(11;19)(q21;p 13) translocation in mucoepidermoid carcinoma creates a novel fusion product that disrupts a Notch signaling pathway,” Nat. Genet. (Advanced Online publication): 1-6 (2003). In particular, at (11;19) translocation has been observed in some cancers of mucoepidermoid origin. In such cases, this may be the sole cytogenetic alteration. This chromosomal translocation has been noted to result in the expression of a chimeric gene, called Mect1-MAML2. Nucleotide sequencing identified the chimeric species as comprising exon 1 of the novel gene at 19p12-13 (Mect1) fused in-frame to exons 2-5 of MAML2. A further description of the Mect1-MAML2 fusion product is contained in commonly-owned, co-pending international patent application no. PCT/US02/021344, the disclosure of which is hereby incorporated in its entirety by reference. The sequence of Mect1-MAML2 has been fully elucidated, and its sequence is available from GenBank as Accession No. AY040324.1 (see also FIG. 1).
Full-length MAML2 appears to function as a CSL-dependent transcription co-activator for ligand-stimulated Notch, much like Drosophila melanogaster Mastermind and MAML 1 factors. In particular, these Mastermind-like transcriptional co-activators form a complex in the nucleus with the intracellular domain of an activated Notch receptor (ICN) and the bifunctional transcription factor CSL.
Recently, a putative function for Mect1 was identified—Mect1 appears to be a member of a conserved family of co-activators that enhance CRE-dependent transcription via a phosphorylation-independent interaction with the bZIP DNA binding/dimerization domain of CREB. Mect1 recruitment does not appear to modulate CREB DNA binding activity, but rather enhances the interaction of CREB with the TAFII 130 component of TFIID following its recruitment to the promoter. CREB belongs to a group whose phosphorylation enhances their transactivation potential. The CREB transactivation domain is bipartite, consisting of kinase-inducible and constitutive activators that function cooperatively in response to cAMP agonist. For a further discussion of the function of Mect1 (also called TORC for Transducers of Regulated CREB activity), see Conkright et al., “TORCs: Transducers of Regulated CREB Activity,” Molecular Cell 12: 413-423 (2003), and lourgenko et al., “Identification of a family of cAMP response element-binding protein coactivators by genome-scale functional analysis in mammalian cells,” Proc. Natl. Acad. Sci. (Early Edition, 2003).
Also recently reported are double-stranded RNA molecules for the inhibition of translation of particular gene products. RNAi is an evolutionarily conserved phenomenon and a multistep process that involves generation of active small interfering RNA in vivo through the action of an RNase III endonuclease, Dicer. The resulting short RNA molecules mediate degradation of the complementary homologous RNA. General description of RNAi compositions and methodology have been discussed in, e.g., Sui et al., “A DNA vector-based RNAi technology to suppress gene expression in mammalian cells,” Proc. Natl. Acad. Sci. 99(8): 5515-5520 (2002), and U.S. Pat. No. 6,506,559 (Fire et al.), the disclosures of which are hereby incorporated in their entirety by reference.
A further technique, which also has been developed, is the use of siRNAs (small interfering RNA) to induce gene-specific suppression. The siRNAs are long enough to induce gene-specific suppression, but short enough to evade the host interferon response. The host interferon response is an antiviral defense mechanism that includes the production of interferon, resulting in non-specific degradation of RNA transcripts and a general shutdown of host cellular protein synthesis. See, Shi, “Mammalian RNAi for the masses,” TRENDS Genet. 19(1): 9-12 (2003), incorporated herein in its entirety by reference.
The invention provides methods and compositions for inhibiting the translation of the Mect1-MAML2 chimeric gene. This and other objects and advantages, as well as additional inventive features, will be apparent from the description of the invention provided herein.